OUR reserves of the immune-boosting vitamin D can fall dangerously low at this time of year and this is what you can do about it

In these dark days are you feeling drained of energy? Some experts might suggest you’ve hit your D-day, the time of year when your reserves of vitamin D are so depleted by a lack of sunshine it is affecting your health. But others could say the growing interest in the so-called sunshine vitamin is misplaced.

A recent meta-analysis, a super study which pools data from previously published research, reported that despite a clear association between low levels of vitamin D and an increased incidence of heart disease, diabetes and other conditions there is no evidence that taking vitamin D supplements protect against these problems. Case closed you might think, except that closer scrutiny of the Lancet study shows it actually found “slight gains in survival” when older people take top-up vitamin D and experts argue the debate is far from over.

Professor Simon Pearce, a vitamin D expert based at Newcastle University, says: “This meta-analysis doesn’t tell you that much because they are taking data collected for one reason and using it for another.”

US-based academic and internationally renowned vitamin D expert Dr Michael Holick is even more sceptical, arguing that the meta-analysis was based on poor studies.

“The scientific term for it is ‘silly’,” he says. “Basically all they have done is rehash old studies but most of those studies are meaningless because they used sub-optimal doses of vitamin D.”

Dr Holick believes that adults need a daily top-up of at least 75mcg and that’s the dose he takes every day. However the 290 trials collated for the meta-analysis used much less with daily doses ranging from 20 to 50mcg.

WHY WE’RE DEFICIENT IN VITAMIN D

Unlike any other nutrient we can’t get enough vitamin D from food alone no matter how well we eat. Instead we make it from sunshine which means the further away from the Equator we live and the more time we spend indoors the higher the risk of deficiency.

The reality is that if you live north of Birmingham it is impossible to make vitamin D from October to March and even in the most southerly parts of Britain there is not enough sunlight to synthesise it for around three months during the winter.

Working in an office also undermines our ability to build up the reserves needed to get through the winter because even at the height of summer there are only four hours a day from 11am to 3pm when it is bright enough to make vitamin D. Professor Pearce says: “We think of the UK as being parallel to New York City but we’re more in line with Alaska. We are a lot further north than we realise.”

HOW A LACK OF SUN MAKES US SICK

Like Dr Holick, Professor Pearce also takes a vitamin D supplement and says there is no doubt we need the nutrient for healthy bones.

“There is absolutely 100 per cent cast iron evidence that lack of vitamin D has adverse effects on musculoskeletal health. That is unequivocal.”

He says: “There is also pretty good evidence linking low vitamin D to certain cancers in particular bowel cancer and Type one diabetes, as well as some autoimmune diseases.”

Dr Holick believes there is also strong evidence of a link between low vitamin D and heart disease, asthma and other allergies, depression, dementia, pregnancy complications and even schizophrenia.

“Population studies have suggested that adequate vitamin D is also critical for the prevention of various solid tumours including prostate, breast, ovarian and colon cancers.”

Further evidence of the link between sunshine and health can be seen in the way geography can influence the risk of multiple sclerosis, an autoimmune condition which damages nerves in the spinal cord and brain.

Around 127,000 people in the UK have MS but the further north you live the greater the risk. In England and Wales around one in 1,000 people has MS but in Scotland it is twice that number while the Orkney Islands, one of the most northerly parts of the UK, has the highest incidence in the world with around four in 1,000 people affected.

Similar patterns have been mapped for some cancers. A European Prospective Investigation into Cancer and Nutrition (EPIC) study which tracks the health of more than 520,000 people across Europe reported a “strong” association between low vitamin D – levels in the blood of less than 25 nmol/l – and bowel cancer which kills around 15,000 people a year in the UK.

A Canadian study of 1,200 women found that those who regularly took a vitamin D supplement cut their cancer risk by 60 per cent.

Professor Kefah Mokbel, a surgeon at the London Breast Institute, a private centre based at The Princess Grace Hospital, argues: “This is a low-cost, cheap intervention and there is no toxicity from taking it.”

Low Vitamin D levels are linked to mental health problems such as depression and schizophrenia [GETTY]

IMMUNE BOOST

Evidence of the importance of vitamin D may be new but we have long recognised the healing power of the sun.

Victorian doctors routinely prescribed rest in a sanatorium soaking up the sun as a cure for tuberculosis, a successful treatment which fell out of favour with the discovery of antibiotics.

Now scientists are beginning to understand the way sunlight and vitamin D influence our ability to fight infection and disease.

Danish researchers have found that vitamin D arms and triggers T cells, the foot soldiers of our immune system which destroy viruses, bacteria and other threats.

Professor Carsten Geisler of the Department of International Health, Immunology and Microbiology at the University of Copenhagen, Denmark, explains: “If the T cells cannot find enough vitamin D they won’t even begin to mobilise.”

COULD YOU BE LOW?

Vitamin D deficiency is almost “universal” in the UK in winter warns Dr Robert Moy, a British paediatrician and former adviser to the World Health Organisation.

Like Professor Pearce and Dr Holick he also takes extra vitamin D, 10mcg for around six months of the year, the amount recommended by the UK’s chief medical officer for at-risk adults.

According to the NHS, anyone who does not get much sun because they cover up or spend a lot of time indoors is at risk of deficiency including over-65s, babies and children under the age of five, anyone with darker skin and all pregnant and breastfeeding women.

People who are overweight are also likely to be deficient although scientists don’t agree on whether excess weight causes the deficiency or if low levels of the vitamin lead to weight gain.

WHAT LEVEL IS BEST?

Vitamin D status is determined by the amount circulating in your blood.

Extreme deficiency, anything below 25 nmol/l, requires high doses to restore levels and long-term supplementation to keep them healthy. If your levels are this low there may be symptoms such as bone pain, deformities such as rickets, and seizures.

In winter many people are likely to have levels between 25 and 50 nmol/l which is categorised as insufficiency and requires long-term supplementation.

According to Dr Holick: “No one, unless they are a lifeguard or sun worshipper, will have a blood level above 50 unless they take supplements.”

Yet symptoms of insufficiency are much harder to spot. Dr Holick says: “Often in winter time people get more aches and pains and feel more stiff in the morning. Those are all classic signs of vitamin D deficiency.

“I have many patients who come to me with these non-specific symptoms and put it down to the fact they are getting older or working harder. However after they take vitamin D they find their energy levels are higher and they feel better.”

A level of 50 nmol/l or more is ideal while 250 nmol/l or more is potentially toxic although Dr Holick says that not even very high doses of vitamin D will push concentrations up this much. On average he prescribes 75mcg a day.

TUCK IN TO TOP UP

While diet can’t provide all your vitamin D needs it can add a useful top-up:

Oily fish such as mackerel, salmon and herring is one of the best sources of vitamin D but farmed fish, eg most supermarket salmon, contains less than fish caught in the open seas.

Eggs provide an excellent top-up. Tests by the Department of Health confirm that a large egg now contains just under 2mcg of vitamin D, 70 per cent more than 30 years ago. The increase is due to hens being given feed fortified with vitamin D.

Red meat has useful amounts because animals which graze outside build up stores of vitamin D in their fat. Dietician Carrie Ruxton says: “It’s almost as if Mother Nature has given us a clue because vitamin D deficiency is at its worst during the winter when there is no better time to tuck into a hearty beef stew or lovely lamb hotpot.”

Breakfast cereals are increasingly being fortified with vitamin D. Check nutritional information on the pack but a 30g serving could provide around 1mcg.

Yogurt and dairy drinks may have additional vitamin D. Check nutrition information on the pack. One pot of the yogurt Calin+ contains 5mcg.